Lithium Ion Battery Electrolyte for High-Temperature Cycle Stability
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Solution Overview
Problem
Lithium ion secondary batteries face challenges in maintaining capacity and reducing volume increase, especially in high-temperature environments, and fluorinated solvents used to mitigate gas generation have low dielectric constants, making it difficult to dissolve lithium salts effectively.
Innovation Solution
A lithium ion secondary battery design incorporating a negative electrode with silicon, silicon oxide, and carbon, and an electrolyte liquid comprising a chain-type fluorinated ester compound and a chain-type fluorinated ether compound, which improves cycle properties and reduces volume increase by enhancing lithium ion conductivity and compatibility with carbonate solvents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If fluorinated solvents are used to reduce gas generation, then gas generation is reduced, but lithium salt dissolution becomes difficult due to low dielectric constant
Solution Approach 1:
The patent combines fluorinated solvents with carbonate solvents in a mixed electrolyte system. The carbonate solvent component provides high dielectric constant for effective lithium salt dissolution, while the fluorinated solvent component suppresses gas generation. This merging of two solvent types allows simultaneous achievement of both benefits.
Solution Approach 2:
The electrolyte uses a composite solvent system comprising fluorinated solvents and carbonate solvents. This composite approach leverages the complementary properties of each solvent type: fluorinated solvents for gas suppression and carbonate solvents for ion conduction and salt dissolution, creating an electrolyte with balanced performance.
2Quantity of substance
If silicon is used as negative electrode active material to increase capacity, then energy density is improved, but volume increase occurs during charge/discharge cycles
Solution Approach 1:
The patent applies carbon coating locally on the surface of silicon particles. This carbon layer has different properties from the bulk silicon, providing a stable protective shell that constrains volume expansion during lithiation/delithiation cycles while allowing lithium ion transport, thus maintaining high capacity benefits of silicon without the volume increase problem.
Solution Approach 2:
The patent embeds silicon particles within a carbon matrix or coating structure. The carbon shell acts as a container that accommodates the volume changes of silicon during charge/discharge, similar to how nested dolls fit within each other. This nested structure allows silicon to expand and contract without causing macroscopic volume increase of the electrode.
3Quantity of substance
If 5V class positive electrode active material is used to increase operating potential, then energy density is improved, but cycle life and stability deteriorate
Solution Approach 1:
The fluorinated solvent acts as an intermediary between the 5V positive electrode and the electrolyte. It forms a stable interfacial layer that mediates the interaction between the high-potential electrode and the electrolyte, preventing direct harmful reactions while allowing ion transport, thus enabling stable operation at 5V potentials.
Solution Approach 2:
The patent changes the chemical composition parameters of the electrolyte by introducing fluorinated solvents with specific molecular structures. This parameter change in the electrolyte composition allows it to stabilize the interface with 5V positive electrode materials, enabling high energy density operation with improved cycle life.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The battery achieves excellent cycle properties and reduced volume increase even in high-temperature environments, with improved lithium ion conductivity and compatibility, effectively addressing the limitations of fluorinated solvents and enhancing energy density.
Implementation Method 1
an electrolyte liquid comprising a chain-type fluorinated ester compound represented by following formula (1) and a chain-type fluorinated ether compound represented by following formula (2)... improves cycle properties and reduces volume increase by enhancing lithium ion conductivity
Implementation Method 2
metal oxide (b) that can absorb and desorb lithium ion... carbon material (c) that can absorb and desorb lithium ion
Implementation Method 3
a metal particle that can be alloyed with lithium... using silicon or silicon oxide as a negative electrode active material
Data Source
AI summary
The object is to provide a lithium ion secondary battery which has an excellent cycle property even in high-temperature environment and which has small volume increase. An exemplary embodiment of the invention is a lithium ion secondary battery, comprising: a positive electrode, a negative electrode comprising a negative electrode active material, and an electrolyte liquid; wherein the electrolyte liquid comprises a chain-type fluorinated ester compound represented by a predetermined formula and a chain-type fluorinated ether compound represented by a predetermined formula; wherein the negative electrode active material comprises metal (a) that can be alloyed with lithium, metal oxide (b) that can absorb and desorb lithium ion, and carbon material (c) that can absorb and desorb lithium ion; and wherein metal (a) is silicon, and metal oxide (b) is silicon oxide.